The present invention relates to a thermoelectric printer which in particular is able to implement a high quality thermoelectric printing, regardless of the sizes of a take-up diameter of the ink coated film used for thermoelectric printing and taken up by a take-up shaft.
Description of the Related Art
For example, for prints, such as large size price tags at a supermarket, a thermoelectric printer is used. This thermoelectric printer is able to print on rather large size papers in clear, by a simple way and in short time.
FIG. 1 is a perspective diagram of a main part of an ink coated film feeding mechanism 100 of the conventional thermoelectric printer. As shown in FIG. 1, over a rectangular plate type thermal head 101, a platen 103 which presses and transfers ink on an ink coated flm 102 to a paper 107 is disposed. The ink coated film 102 is taken up by a take-up shaft 104 rotating in a fixed torque to the counterclockwise direction. Between the take-up shaft 104 and the thermal head 101, a ribbon feed roller 105 which drives the ink coated film 102 with friction by the same fixed torque of the take-up shaft 104 to the counterclockwise direction and gives the ink coated film 102 tension and carries the ink coated film 102 to the direction of an arrow X.sub.1 is disposed. At the below right of the thermal head 101, a ribbon brake roller 106 which gives the ink coated film 102 a certain brake to give tension to the ink coated film 102 is disposed.
At the upper left of the thermal head 101, a first paper feed roller 108 constituted of a pair of rollers which carries the paper 107 in putting between the rollers by friction to the direction of an arrow X.sub.2 in a fixed speed is disposed. At the upper right of the thermal head 101, a second paper feed roller 109 constituted of a pair of rollers which carries the paper 107 in putting between the rollers by friction to the direction of an arrow X.sub.2 in a fixed speed and works together with the first paper feed roller 108 is disposed. By the rotating control of a motor of a controller, this motor is not shown in FIG. 1, the take-up shaft 104, above mentioned rollers 105, 106, 108 and 109 are rotated, and the ink coated film 102 is carried to the direction X.sub.1 and the paper 107 is carried to the direction X.sub.2. While this carrying process, the ink coated film 102 and the paper 107 are pressed between the thermal head 101 and the platen 103 and the ink coated on the ink coated film 102 is transferred to the paper 107 by the thermoelectric printing. In this case, it is a premise that the ink coated film 102 and the paper 107 are carried on the thermal head 101 by the same feed torque.
In the conventional ink coated film feeding mechanism, the ink coated film 102 is taken up by the take-up shaft 104 with a fixed torque. However, the take-up diameter between the beginning and the ending of the take-up shaft 104 is different, therefore the feed torque applying to the ink coated film under taken up changes.
At this, the following formula (1) is formed in the relation among the feed power F applying to the ink coated film under taken up, the rotating torque T of the take-up shaft, the take-up diameter D increasing by the taking up of the ink coated film, the friction coefficient .mu. between the ribbon feed roller and the ink coated film, and the power P which the ribbon feed roller presses and touches the ink coated film. EQU F=(2T/D)+.mu.P (1)
FIG. 2 is a graph showing the relation between the take-up diameter D and the feed power F. The unit of the take-up diameter D is mm and the unit of the feed power F is gram. As shown in FIG. 2, at the beginning of the take-up, the take-up diameter is small and the feed power is large, the tension of the ink coated film on the thermal head becomes too large and the problem that creases are formed on the ink coated film occurs.
On the contrary, at the ending of the take-up, the feed power F applying to the ink coated film becomes small, at the time when the paper is putted on the ink coated film on the thermal head, the slip between the paper and the ink coated film occurs, and the paper is stained by unnecessary ink and the thermal head is stained too, these problems occur. To solve these problems caused by the change of the feed power, as shown in FIG. 1, the conventional thermoelectric printer provides a clutch means 110 between the ribbon feed roller 105 and a roller rotating driving means which drives the ribbon feed roller 105, this roller rotating driving means is not shown in FIG. 1. This clutch means 110 is constituted of a first clutch plate 110a joining to the ribbon feed roller 105 by gears and a second clutch plate 110b glued a slipping material 110c. In this, this slipping material 110c is made of synthetic resin with special surface treatment. The second clutch plate 110b is directly joined to the roller rotating driving means which is not shown in FIG. 1.
As mentioned above, the take-up shaft 104 and the ribbon feed roller 105 are rotating by a fixed torque respectively, however at the case that the feed power under taken up is large, the clutch means 110 slips the ribbon feed roller 105 and the rotating torque of the roller rotating driving means is not transferred and prevents creases from occurring. On the contrary, the feed power under taken up is small, the clutch means 110 transfers the rotating torque of the roller rotating driving means to the ribbon feed roller 105 and makes the ink coated film have tension and the occurrence of the stain is prevented.
However, in the above mentioned feed power changing solution using the special slipping material, the value starting slip has a variation, the problem of the stain and creases is not solved completely.